Ball bearings, such as the ball bearing 1 shown in FIG. 1, are widely used for supporting various rotating parts, such as the bearings of various rotating mechanical devices. This ball bearing 1 comprises an inner race 3, that has a inner-race track (also referred to as raceway) 2 formed around its outer peripheral surface, an outer race 5, that has an outer-race track 4 formed around its inner peripheral surface, which are located such that they are concentric, and a plurality of balls 6 that are located between the inner-race track 2 and outer-race track 4 such that they can rotate freely. In the example shown in the figure, the inner-race track 2 and outer-race track 4 are both formed in a deep groove shape. In addition, the plurality of balls 6 are held in pockets 8 that are formed in the retainer 7 such that they can rotate freely.
The retainer 7 of the ball bearing 1 shown in FIG. 1 is called a wave-shaped pressed retainer, and is formed by combining a pair of elements 9 that are obtained by pressing a some kind of metal sheet material into a wave-shaped circular ring. Both of these elements 9 are formed with concave sections 10 that form pockets 8 at a plurality of locations around in the circumferential direction.
This pair of elements 9 come together at sections that are separated from the concave sections 10 and are joined and fastened together by a plurality of rivets 11 at these sections to form the retainer 7 which is ring shaped and has the pockets 8 around in the circumferential direction.
The middle section on the inside surface of the concave sections 10 has a radius of curvature that is slightly larger than the radius of curvature of the outside surface or rolling surface of the balls 6, and forms a partial spherical and concave retaining surface 12. Therefore, when the pair of elements 9 come together, the concave sections 10 come together to form the pockets 8.
The retainer 7 shown in FIG. 2, called a crown-shaped retainer, comprises a ring-shaped main section 13 that is made of synthetic resin, in which pockets 8 are formed at a plurality of locations around in the circumferential direction for holding the balls 6 such that they can rotate freely. In the case of this kind of crown-shaped retainer 7, a plurality of elastic pieces 14 are arranged around the main section 13 such that there is a space between them, and the pockets 8 each is defined by the opposing side surfaces of a pair of elastic pieces 14 and a spherical-shaped concave section 15 that is formed between the pair of elastic pieces 14 on the surface on one side (top surface in FIG. 2) in the axial direction (vertical direction in FIG. 2) of the main section 13.
The radius of curvature of this concave section 15 is slightly larger than the radius of curvature of the outer surface of the balls 6. The side surfaces of the elastic pieces 14 and the concave section 15 form a concave retaining surface.
When assembling the ball bearing, the balls 6 are inserted in between the pair of elastic pieces 14 by elastically pressing open the space between the tip ends of the pair of elastic pieces 14. As soon as balls 6 have been pressed into place, the elastic pieces 14 elastically return to their original shape to hold the balls 6 inside the pockets 8, and these balls 6 are then held between the inner-race track 2 and outer-race track 4 (see FIG. 1) such that they rotate freely.
When using a ball bearing 1 equipped with the retainer 7 described above, the inner race 3 rotates freely with respect to the outer race 5 due to the rolling motion of the balls 6. At this time, the balls 6 revolve around the inner race 3 as they rotate. Moreover, the retainer 7 rotates around the inner race 3 at the same speed that the balls 6 revolve around the inner race 3.
Grease is filled in the section between the outer peripheral surface of the inner race 3 and the inner peripheral surface of the outer race 5 in order that they rotate smoothly with respect to each other. Also, together with preventing the generation of vibration or noise in the ball bearing 1, the grease prevents trouble due to seizure etc. It is not shown in FIG. 1, however the openings on both ends in the axial direction of space 16 where the balls 6 are located between the outer peripheral surface of the inner race 3 and the inner peripheral surface of the outer race 5 are covered by a pair of seal plates 17 of the contact type as shown in FIG. 6, or of the non-contact type, and these seal plates 7 prevent grease from leaking from the space 16 as well as prevent foreign matter such as dirt from getting inside the space 16.
The outer peripheral edges of the seal plates 17 fit into seal grooves all the way around the inner peripheral surface on both ends of the outer race 5, and the inner peripheral edges come in contact with or come very close to the outer peripheral surface on both ends of the inner race 3.
In the case of the ball bearing 1 with a retainer 7 as described above, vibration of the retainer 7 may be caused even when the ball bearing 1 is filled with or supplied with the required amount of lubricant, so noise or vibration, called ‘retainer noise’ may occur in the ball bearing 1 with this retainer 7. The vibration of this kind of retainer 7 is due to large movement of the retainer 7 with respect to the balls 6, which is caused by the sliding friction between the balls 6 and the retainer 7.
Conventionally, generation of this kind of retainer noise was suppressed by making the gap between the inner surface of the pockets 8 and the rolling surface of the balls 6 smaller in order to reduce the amount of movement of the retainer 7 with respect to the balls 6.
However, by just reducing the amount of movement of the retainer 7 with respect to the balls 6, the grease 20 (see FIG. 5 and FIG. 6) filled in the space 16 where the balls 6 are located presses against the seal plate 17 from inside the space 16, making it easy for the grease to leak out. Also, it becomes easy for retainer noise due to the shape of the inner peripheral surface of the pockets 8 to occur. The reason for this is explained using FIG. 3 and FIG. 4.
In the case of the retainer 7 in the prior art structure, nearly the entire inner peripheral surface of the pockets 8 of the retainer 7 is a spherical concave shape having a radius of curvature that is slightly larger than the radius of curvature of the rolling surface (also referred to as rolling contact surface) of the balls 6. Also, the edge 18 on the opening of the pockets 8 comes very close to the rolling surface of the balls 6, as shown in FIGS. 3 and 4.
Moreover, by making the gap between the inner surface of the pockets 8 and the rolling surface of the balls 6 smaller in order to suppress the retainer noise, it becomes difficult for the grease 20 to enter the clearance 19 between the rolling surface of the balls 6 and the concave surface 12 of the retainer 7 (in the case shown in FIG. 1), or between the rolling surface of the balls 6 and the side surfaces of the elastic pieces 14 and the concave section 15 (in the case of the retainer 7 shown in FIG. 2).
In other words, the grease 20, that adheres to the rolling surface of the balls 6 and that tries to get into this clearance 19 from the surrounding space as the balls 6 roll, is scraped off by the edges 18 on the openings of the pockets 8, and as shown by dotted areas in FIGS. 5 and 6, adheres to the edges 18 on the openings. The grease 20 that adheres to the edges 18 of the openings in this way builds up on the edges 18 of the openings as the balls 6 roll, making it difficult for grease 20 to get into the clearance 19.
Also, of the grease 20 that builds up on the edges 18 of the openings in this way, the grease 20 that builds up on the inner peripheral surface of the retainer 7 presses the inner peripheral edges of the seal plates 17 from inside the space 16, and separates the inner peripheral edges of the seal plates 17 from the outer peripheral surface on both ends of the inner race 3 (in the case of the contact-type seal plate) to leak out of the space 16, or leaks out of the space 16 through the small gap that exists between the inner peripheral edges of the seal plates 17 and the outer peripheral surface on both ends of the inner race 3 (for a non-contact-type seal plate). Therefore, over a long period of use, the amount of grease 20 that remains in this space 16 gradually decreases, and there is a possibility that abnormal wear or seizure will occur due to poor lubrication.
Leakage of grease 20, that is the cause of problems such as these, is more severe during use when the inner race 3 is still and the outer race 5 is rotated, than when the outer race 5 is still and the inner race 3 is rotated. The reason for this is, that when the outer race 5 is rotated, the grease 20 that has reached the inner peripheral surface of the outer race 5 is easily fed to the outer-race track 4 by the centrifugal force, and when in this area of the outer-race track 4, the grease 20 adheres to the rolling track surface of the balls 6 (which is the part of the rolling surface of the balls 6 that makes rolling contact with the inner-race track 2 and outer-race track 4) to easily move radially inward within the retainer 7.
Since a substantial amount of the grease 20 that adhered to the rolling surface of the balls 6 adheres to the edge 18 of the opening, it becomes difficult for the grease 20 to get inside the clearance 19, so that it becomes impossible to adequately suppress friction and vibration in the area of sliding contact between the retainer 7 and the balls 6, thus vibration and noise occurs.
Construction of a ball bearing in which the grease, that adheres to the inner peripheral surface of the retainer, is directed to the outer peripheral surface of the retainer, thereby preventing leakage of the grease from the inner peripheral edge of the seal plates has been known, such as disclosed in Japanese Patent Publications Toku Kai Hei 8-270662 and Jitsu Kai Hei 7-10556.
Of these, in the construction disclosed in Toku Kai Hei 8-270662, part of the seal lip of the seal plate, made of elastic material, comes close to the outer peripheral surface of the inner race, and is formed to protrude to the ball side, making a protruding section, so that the grease, that adheres to the inner peripheral surface of the retainer, is directed to the outer peripheral surface of the retainer. Also, in the construction disclosed in Jitsu Kai Hei 7-10556, the grease that adheres to the inner peripheral surface of the retainer is directed to the outer peripheral surface of the retainer by a slinger that fixedly fits around the outer peripheral surface of the inner race.
Furthermore, construction in which there is a seal lip on the inner peripheral edge of the seal plate that comes in contact with the outer peripheral surface of the inner race at multiple locations, or in which there is a multi-stage labyrinth seal between the inner peripheral edge of the seal plate and the outer peripheral surface of the inner race is known. With this prior construction, it is difficult for the grease that adheres to the inner peripheral surface of the retainer to leak out.
Of the prior art constructions mentioned above, in the case of the construction disclosed in Publication of Toku Kai Hei 8-270662, the inner peripheral surface of the protruding section closely faces the outer peripheral surface of the inner race, so it is necessary to strictly regulate the accuracy of the dimensions between the seal plate and the inner race. Particularly, it is necessary to perform finishing such as polishing to the section on both ends of the outer peripheral surface of the inner race that is separated from the inner-race track, which was not necessary originally, so that the manufacturing cost increases. Also, the size of the ball bearing to which this can be applied is limited, and it is difficult to apply the construction to a small-diameter ball bearing, or to a ball bearing that is thin in the axial direction.
Moreover, in the case of the construction disclosed in Publication of Jitsu Kai Hei 7-10556, a separate part or slinger is required just in order to direct the grease to the outside, so that the number of parts increases as well as the number of assembly steps, thus increasing the manufacturing cost. Also, as in the case of the construction disclosed in Publication of Toku Kai Hei 8-270662, the size of the ball bearing to which it can be applied is limited, and it is difficult to apply the construction to a small-diameter ball bearing, or to a ball bearing that is thin in the axial direction.
Furthermore, in the case of the construction of forming a plurality of sliding contact sections, or of forming a multi-staged labyrinth seal, not only does the rotation torque of the ball bearing increase and the heat generated during high-speed operation become severe, but in many cases it is not possible to sufficiently obtain the effect of leak prevention.
Rolling bearings, such as the rolling bearing 1 with seal plate as shown in FIGS. 7 and 8, are used for rotation support of various kinds of mechanical equipment. This rolling bearing 1 with seal plate comprises: an inner race 3 with an inner-race track 2 formed around its outer peripheral surface; an outer race 5, which is concentric with the inner race 3 and that has an outer-race track 4 formed around its inner peripheral surface; and a plurality of rolling element 6 that roll freely between the inner-race track 2 and the outer-race track 4. The plurality of rolling elements 6 are held by a retainer (not shown in the figures) such that they can roll freely. In addition, the outer peripheral edges of seal plates 108 fit in seal grooves 107 that are formed all the way around the inner peripheral surface on both ends of the outer race 5.
These seal plates 108 are formed into a ring shape by reinforcing an elastic member 110 made of an rubber-like elastomer, with a ring-shaped core metal 109 that is made from metal plate such as steel plate. The outer peripheral edge of the elastic member 110 protrudes outward in the radial direction (vertical direction in FIGS. 7 and 8) a little more than the outer peripheral edge of the core metal 109, and this protruding section fits into the seal grooves 107. On the other hand, the inner peripheral edge of the elastic member 110 protrudes sufficiently inward in the radial direction more than the inner peripheral edge of the core 109 to form a seal lip 111.
Moreover, a pair of wall surfaces 114, 115 are formed in the outer peripheral surface on both ends of the inner race 3 to form a seal groove 113, and the end edge 112 of the seal lip 111 comes in contact with the wall surface 115, which is on the inside in axial direction (horizontal direction in FIGS. 7 and 8) with respect to the pair of wall surfaces 114, 115.
In the example shown in the figures, the free state of the elastic member 110 is shown by the solid line, and the state when the seal lip 111 is elastically deformed to come in contact with the wall surface 115 is shown by the dotted line.
The rolling bearing 1 with seal plate, constructed as described above, allows the member attached to the inner race 3 to rotate with respect to the member attached to the outer race 5, due to the rolling of the rolling elements 6. Also, the pair of seal plates 108, whose outer peripheral edges are attached to the inner peripheral surface on both ends of the outer race 5, prevent the grease, filled in the space 16 where the rolling elements 6 are located, from leaking out, and also prevents foreign matter such as dirt or water on the outside from getting into the space 16 where the rolling elements 6 are located.
With the rolling bearing 1 with seal plate described above, there are the following cases when grease leakage may occur.
Specifically, when the rolling elements 6 rotate, the grease that adheres to these rolling elements 6 is scraped off on the inner diameter side of the retainer, and part of that grease is pressed out through the seal grooves 113. The seal lip 111 of the seal plate 108 is elastically deformed by the grease that is pressed out such that it is separated from the wall surface 115 of the seal groove 113, and this causes a small gap between the seal lip 111 and the wall surface 115 and grease leaks out through this small gap.
Moreover, as the pressure inside the space 16 where the rolling elements 6 are located rises due to rolling friction or grease mixing resistance during use, this elastic deformation of the seal lip 111 becomes even greater, and thus grease leakage is even more severe.
In order to prevent grease leakage due to the aforementioned cause, the construction of the seal plate is tailored to improve the seal characteristics. For example, the rolling bearing 1 with seal plate that is disclosed in Japanese Patent Publication Toku Kai Hei 8-226449 is shown in FIG. 9. For the seal plate 108 that is installed in this rolling bearing 1 with seal plate, the angle is controlled between the end edge 112 of the seal lip 111 formed on the inner peripheral edge of the elastic member 110 and the wall surface 115 of the seal groove 113 that this seal lip 111 comes in contact with. That is, when the angle θ 17 between one inclined side surface 117 of the pair of inclined side surfaces 117, 118 of the end edge 112 and the wall surface 115 is made to be 50 to 85 degrees, and the angle θ 18 between the other inclined side surface 118 and the wall surface 115 is made to be 5 to 40 degrees, it is possible to improve the seal characteristics. Also, there is a constricted section 119 that fits all the way along the inner peripheral surface of the elastic member 110 which improve the followability of the seal lip 111 with respect to the wall surface 115.
Moreover, as shown in FIG. 10, it is known in the art that a seal lip 111 on the inner peripheral edge of the elastic member 110 of the seal plate 108 is forked such that this seal lip 111 crosses over the seal groove 113 formed on the outer peripheral surface on the end of the inner race 3, and comes in contact all the way around the circumference at two separate locations in the axial direction on the outer peripheral surface on the ends of inner race 3.
Furthermore, it is not shown in the figures, however, Japanese Patent Publications Toku Kai Hei 7-293571 and Toku Kai Hei 7-139553 disclose a construction where a seal lip on the inner peripheral edge of the elastic member comes in contact with the axially outer one of the pair of wall surfaces of the seal groove, and the length in the radial direction and thickness in the axial direction of this seal lip is controlled in order to maintain the seal characteristics.
Furthermore, Japanese Patent Publication Jitsu Kou Hei 6-27859 discloses a construction where a seal lip similarly comes in contact with the axially outer one of the wall surfaces, and where a variable labyrinth clearance is formed by a different seal lip that moves with the centrifugal force to maintain the seal characteristics.
In the case of this formerly known rolling bearing 1 with seal plate, constructed as described above, the following problems occur. First, in the case of the first example of prior art construction shown in FIGS. 7 and 8, the angle between the end edge 112 of the seal lip 111 and the wall surface 115 of the seal groove 113 is small. In other words, the angle α between the wall surface 115 and the inclined surface 120 of the edge 112 that faces this wall surface 115 is small. Therefore, when the grease is pressed out through the seal groove 113 and enters into the clearance between the wall surface 115 and the inclined surface 120, wedging action occurs as the grease moves in, and it become easy for elastic deformation of the seal lip 111 in the direction that separates it from the wall surface 115 to occur, and thus it is easy for a small gap to occur between the seal lip 111 and wall surface 115. In addition, it becomes easy for surface contact to occur between the end edge 112 of the seal lip 111 and the sliding contact area of the seal groove 113 to occur, making it difficult to maintain stable contact.
Moreover, in the case of the construction disclosed in Japanese Patent Publication Toku Kai Hei 8-226449 and shown in FIG. 9, there is a constricted section 119 formed on the inner peripheral edge of the elastic member 110, so elastic deformation of the seal lip 111 becomes easy, and thus becomes easy for a small gap to occur between the seal lip 111 and the wall surface 115.
Also, since the angle θ 17 between one of the inclined surfaces 117 of the edge 112 of the seal lip 111 and the wall surface 115 of the seal groove 113 is large, the overall dimension in the axial direction of the seal plate 108 increases.
Furthermore, it becomes easy for foreign matter from the outside to build up in the gap between the other inclined surface 118 of the end edge 112 and the side wall surface 115, and this foreign matter presses the seal lip 111 in a direction that separates it from the wall surface 115. Therefore, when this construction is used in cases where the outer race 5 rotates, it particularly becomes difficult to prevent foreign matter from getting inside.
Also, in the case of the construction shown in FIG. 10, it becomes easy for a contact state in the sliding contact section between the outer peripheral surface on the end of the inner race 3 and the edge of the seal lip 111 to be varied due to offset of the center axis of the inner race 3 and outer race 5 that occurs due to external force that is applied during use because of shape and dimensional errors of the seal groove 113, and thus it becomes difficult to obtain stable seal performance.
Moreover, in the case of the construction disclosed in Japanese Patent Publications Toku Kai Hei 7-293571 and Toku Kai Hei 7-139553, the seal lip comes in sliding contact with the axial outer one of the wall surfaces, so it is necessary to form an air hole for releasing pressure in the internal space, and thus it becomes easy for grease to leak from this air hole.
Furthermore, in the case of the construction disclosed in Japanese Patent Publication Jitsu Kou Hei 6-27859, it becomes easy for the seal lip for the labyrinth clearance to become hard due to heat degradation, and thus it becomes impossible to adequately maintain the flexibility of the grease lip for a long period of time, and it is difficult to maintain good seal characteristics over a long period of time.
In this way, of the grease that adheres to the edges of the openings, the part of the grease that builds up on the inner peripheral surface of the retainer is pressed out through the seal groove 113. Also, the seal lip 111 of the seal plate 108 is elastically deformed by the grease that is pressed out in the direction that separates it from the wall surface of the seal groove 113, and this creates a small gap between the seal lip 111 and the wall surface, and grease leaks from this small gap.
Moreover, when the pressure inside the space 16 where the balls 6 are located, due to the rise in temperature caused by rolling friction or mixing resistance of the grease when the bearing is in use, the elastic deformation of the seal lip 111 becomes even greater, and grease leakage becomes more severe. When this kind of grease leakage occurs, the amount of grease that remains in the space 16 gradually decreases over a long period of time, and there is a possibility that abnormal wear or seizure could occur due to poor lubrication.
As mentioned previously, Grease leakage, which is the cause of this kind of trouble, is worse in the case when the inner race 3 is still and the outer race 5 is rotated than in the case when the outer race 5 is still and the inner race 3 is rotated, because the grease 20 adheres to the rolling track surface of the rotating surface of the balls 6, easily moves radially inward within the retainer. The grease that has once entered inside the retainer remains on the outer peripheral surface of the still inner race 3 and it becomes difficult for it to return to the outside.
Construction of a bearing for preventing this kind of grease leakage, such as that disclosed in Japanese Patent Publications Toku Kai Hei 8-270662 and Jitsu Kai Hei 6-73454, has been previously known.
Of these, in the case of the construction disclosed in Toku Kai Hei 8-270662, as shown in FIG. 11, a forked seal lip 111 is formed on the inner peripheral edge of the elastic member 110 of the seal plate 108. Also, of this seal lip 111, the protruding section 214, that protrudes toward the ball 6 comes very close to the outer peripheral surface of the inner race 3.
Also, of this seal lip 111, the end edge of the protruding section 214 that protrudes toward the radially inside comes in sliding contact with the axially outer wall of the seal groove 113 that is formed on the outer peripheral surface of the inner race 3. Furthermore, the tip end surface of the protruding section 214 that protrudes toward the ball 6 is inclined outward in the axial direction as it moves outward in the radial direction.
Moreover, in the case of the prior art construction shown in FIG. 11, an inside shoulder section 215 is formed at a radius greater than the radius of the inner-race track 2 on the outer peripheral surface of the inner race 3 adjacent to the axially outer portion of the inner-race track 2, and the size of the radially inner ring-shaped gap 227 between the inside shoulder section 215 and the inner peripheral surface of the retainer 7, that faces this inside shoulder section 215 in the radial direction, is taken to be L1; and the size at the radially inner end of a ring-shaped gap 217, that is formed between the surface on one axial side of the retainer 7 and the axially inner surface of the seal plate 108, is taken to be L2, where L1≦L2.
Accordingly, in the construction disclosed in Japanese Patent Publication Toku Kai Hei 8-270662, it becomes easy for the grease inside the retainer 7 to flow to the outside of the retainer 7 through the aforementioned ring-shaped gap 217, and thus it is possible to prevent this grease from leaking out through the gap between the seal groove 113 and the seal plate 108.
Also, construction similar to the construction disclosed in Japanese Patent Publication Toku Kai Hei 8-270662 is disclosed in Japanese Patent publication Jitsu Kai Hei 6-73454. However, the construction disclosed in Jits Kai Hei 6-73454 differs from the construction disclosed in Toku Kai Hei 8-270662 in that the dimensions of the ring-shaped gap between the surface on the one axial side of the retainer and the seal plate are not considered.
As described above, in the case the construction disclosed in Japanese Patent Publication Toku Kai Hei 8-270662, grease is prevented from leaking by regulating the size L2 of the radially inner end of the ring-shaped gap 217 such that it is greater than the size L1 in the radial direction of the inner ring-shaped gap 227 (L1≦L2), however, it cannot be said that this prevention of leakage is sufficient.
In other words, in the construction disclosed in Japanese Patent Publication Toku Kai Hei 8-270662, the relationship of the size at other sections of the ring-shaped gap 217, or the size in the radial direction of the radially outer ring-shaped gap, that is formed between the outer peripheral surface of the retainer 1 and the inner peripheral surface of the outer race 5, with the size L1 in the radial direction of the radially inner ring-shaped gap 227 is not particularly taken into consideration. For example, in the construction shown in FIG. 11, the size L3 in the axial direction of the radially middle section of the ring-shaped gap 217, is less than the size L2 of the radially inside end (L3<L2). In addition, the size L4 in the radial direction of the outer ring-shaped gap 228 between the outside shoulder section 218 at a radius less than the outer-race track 4, and the outer peripheral surface of the retainer 7 is less than the size L1 in the radial direction of the inner ring-shaped gap 227 (L4<L1). In this case, the grease does not flow smoothly enough to the radially outside, and there is a possibility that grease radially inside the retainer 7 will build up. In that case, there is a further possibility that grease leakage will not be sufficiently prevented.
Moreover, in the case of the conventional constructions as disclosed in the prior art documents, once the grease enter the seal groove 113 formed in the outer peripheral surface on the ends of the inner race 3, this grease is hindered by part of the seal plate 108 and it becomes easy for the grease to return from inside the seal groove 113 to the side where the ball 6 is. Accordingly, the grease that entered inside the seal groove 113 gradually increases, and finally leaks out through the gap between the seal groove 113 and the seal plate 108.
Moreover, in the case of the conventional constructions as disclosed in the prior art documents, the position relationship in the axial direction between the outside surface in the axial direction of the retainer 7 and the end of the seal groove 113 is not particularly considered, and in the case that the grease inside of the retainer 7 is pressed out in the axial direction, there is a possibility that part of this pressed out grease will easily enter inside the seal groove 113. When part of the grease enters inside the seal groove 113 in this way, it is not possible to adequately prevent grease leakage. Particularly, when this bearing is used in a relatively small device, such as when a ball bearing with seal plate is installed in a device such as a hard disk drive (HDD), grease entering inside the seal groove 113 becomes severe.